1. Field of the Invention
The present invention relates to the field of mass storage technology. More specifically, the present invention relates to methods and systems for improving the storage capacity and throughput of a digital mass storage device, such as a disk drive.
2. Related Art
Digital information can be stored magnetically and optically on rotating storage media often called xe2x80x9cdisk mediaxe2x80x9d or platters. The digital storage media can be removable, as in the case of a floppy disk or optical compact disk (CD) or the platters can be non-removable such as in a hard disk. The digital information maintained in this disk storage media is stored in annular shaped tracks that are positioned at different radii from the center of the disk media. Several arc-shaped sectors can reside within each track. The digital information is read from the disk media by a head disk assembly (HDA) which contains a head that is positioned over the tracks of the rotating disk media. Disk drives that are used to store and retrieve audio/video digital information are called AV drives.
Data can be recorded using a constant linear velocity (CLV) technique in which the data density recorded per linear inch of the disk media is constant but the media spins at different rates depending on the radius of the head. The second technique is the constant angular velocity (CAV) technique. In both techniques, the density (e.g., bits/inch) of the information stored within the tracks is constant. In CLV technique, as the head of the disk drive moves across the tracks of the disk media, the rotation speed of the disk media is varied by the disk drive to maintain a constant linear velocity of the head with respect to the recorded information. As the head moves toward the center, the rotation speed is increased because the circumferences of the inner tracks are smaller than the circumferences of the outer tracks. By increasing the rotation speed, the linear velocity, and therefore the data rate, is held constant in the CLV technique. Conversely, in the CAV technique, the rotation speed of the disk media is held constant regardless of the track position of the head. Therefore, in the CAV technique, the data rate of digital information accessed by the head decreases as the read head travels from the outer tracks of the disk media to the inner tracks.
The CLV reading technique is not particularly advantageous because each time the head is moved from one position to another, e.g., in response to a xe2x80x9cseekxe2x80x9d command, the rotation speed of the disk media needs to be adjusted for the new position. During a xe2x80x9cseekxe2x80x9d command, the head of the disk drive is instructed to move from its current position to a new position in order to access digital information from the disk media. In the CLV technique, the rotation speed of the disk media must be adjusted based on the new track position of the head. While the head can be rapidly positioned from its current position to the new position, it takes longer for the spindle motor of the disk drive to reach the target rotation speed for the new head position. Therefore, reading/writing random accessed information from and to a disk media using the CLV technique requires many adjustments to the rotation speed of the disk media and this may severely reduce data throughput.
As result, the CLV technique is disadvantageous for recorded computer information because this information may require many seek commands during retrieval; for each seek, the access time is increased due to the additional time required for the spindle motor to reach its target rotation speed. Moreover, because the rotation speed of the disk media varies based on the head position, the disk drive using the CLV technique requires an advanced speed controllable spindle motor with costly associated control circuitry. Lastly, because the hard drive using the CLV technique is constantly accelerating its spindle motor, torque is required using the CLV technique, which increases the overall power consumption of the disk drive. This makes the CLV technique disadvantageous for battery operated (e.g., portable laptop) computer systems that have limited power stores and are extremely heat sensitive.
However, current CAV techniques also have disadvantages. Because the CAV disk drives operate at a constant angular velocity, the data throughput rate changes depending on the region of the disk media at which the head is positioned. The data throughput rate at the inner tracks of the disk media is significantly lower than the data throughput rate achievable at the outer tracks of the platter. The data throughput rate difference is typically large, with the inner tracks"" data rate frequency representing only half of the outer tracks"" data rate. As a result, CAV disk drives often operate at a reduced capacity in order to meet certain data throughput rate requirements of some audio/video applications that require high sustained data throughput for normal operation.
For instance, if a particular application demands a high data throughput that cannot be met or maintained using the inner track regions of the disk media, then the disk drive maker will not allow data storage on the inner track regions. Although the data throughput rate is increased, this limitation will inherently reduce the storage capacity of the disk drive because a large potion of the available disk media will not be used by the disk drive. In effect, hardware manufacturers normally forgo the use of the inner surfaces of the media, thereby reducing the potential capacity of the drives, in an effort to guarantee acceptably high data throughput of their drivers.
Accordingly, what is needed is a disk drive having a high and maintained data throughput rate that also makes use of the potential storage capacity of the disk media in that the inner track regions as well as the outer track regions are used to store data thereon. That is needed further is a disk drive having improved storage capacity and high uniform data throughput rate that also uses constant angular velocity (CAV) techniques. What is also needed is a disk drive having the above characteristics that is used for the storage and retrieval of audio/visual digital information. What is yet needed is a disk drive having the above characteristics that can be implemented within a computer system. As described herein, the present invention offers these advantages and others not recited above but made clear within discussions of the present invention to follow.
Methods and systems are described herein for improving the storage capacity and data throughput of a digital mass storage device, such as a disk drive. The novel optimizations can be applied to a disk drive, either a hard disk drive or a disk drive having removable media, such as magnetic and optical disk drive technologies. The present invention provides at least two disk drive heads for reading and writing information from two different spinning disk media surfaces, e.g., platters or disks. If the disk drive is a read-only device, then the heads only perform the read function. The drive mechanism is a constant angular velocity drive meaning the rotational speed of the disk media is constant regardless of the head""s position with respect to the disk media. In operation, during a media transfer, the first head accesses data by starting at the outside regions (xe2x80x9chigh track ratesxe2x80x9d) of the circular (xe2x80x9cdiskxe2x80x9d) media and traversing inward towards the inner regions (xe2x80x9clow track ratesxe2x80x9d). The second head, traversing in the opposite direction, but in synchronization with the first head, starts accessing data at the inner regions of its disk media and traverses towards the outer regions.
Although the data throughput rate of each head varies as the head moves across the tracks, the combined data throughput rate of the two heads remains substantially constant in accordance with the present invention. A data file is portioned and its portions are accessed using both heads combined to provide a uniform and high data throughput rate. The sectors are specially mapped and the data is interleaved to provide a maximum throughput rate. Storage capacity is increased because much, if not all, of the inner regions of the disk media are used in the present invention while still maintaining a high and uniform data throughput rate.
More specifically, an embodiment of the present invention includes a digital storage device comprising: a first head for writing digital data on tracks of a first disk media, the first head moving across the tracks of the first disk media in a first direction; a second head for writing digital data on tracks of a second disk media, the second head moving across the tracks of the second disk media in a second direction opposite to the first direction; and a multiplexer circuit for receiving a digital data stream and for supplying first portions of the digital data stream to the first head and second portions of the digital data stream to the second head, wherein respective size ratios of respective first and second portions are based on corresponding track position ratios of the first and second heads. Embodiments include the above and wherein the first head and the second head write digital data with a substantially constant combined data throughput rate as a result of the respective size ratios and wherein the first direction the first head is from outer tracks to inner tracks of the first disk media and wherein the second direction of the second head is from inner tracks to outer tracks of the second disk media. Embodiments include the above and further comprising a mechanism for spinning the first and second disk media at a constant angular velocity.
Embodiments of the present invention also include a digital storage device comprising: a first set of heads coupled to a first actuator and for reading digital data off of tracks of a first disk media, wherein the first set of heads moves in a direction from outer tracks to inner tracks of the first disk media; a second set of heads coupled to a second actuator and for reading digital data off of tracks of a second disk media, wherein the second set of heads moves from inner tracks to outer tracks of the second disk media in opposite direction to the first set of heads; and a demultiplexer circuit for receiving the digital data from the first set of heads and from the second set of heads and for supplying a single digital data stream therefrom wherein digital data is supplied from the first and second set of heads at a combined throughput rate that is substantially constant.